Apparatus and method for cleaning out an underground well

ABSTRACT

Method has been provided for cleaning a vertical, deviated or horizontal underground well. In which a maintenance tubing having a cleaning head at its end is lowered into a production pipe for suction of sediments. At a certain level above the region of the well to be cleaned, a hydraulic isolation device is installed in the annulus between the maintenance tubing and the production pipe. Fluid is injected into the annulus to activate the hydroejector which is located above the hydraulic isolation device to cause the suction of the sediments. The sediments downhole therefore can be cleaned out without introducing foreign fluid downhole.

BACKGROUND OF THE INVENTION

The present invention relates to a method of cleaning out an undergroundwell and to an apparatus for applying said method.

When well bottom deposits, particularly sandy sediments ofunconsolidated formations, are present, a first method consists in usingdrilling apparatus to recondition the production tubing at stratumlevel. The application of this method is very onerous because theequipment installed has to be dismantled and a new completion isnecessary after the cleaning operation. In order to avoid having toresort to such heavy "workover" operations, various means are availablefor the concentric maintenance of well bottoms.

In particular, from U.S. Pat. No. 4,671,359 a cleanout system is knownfor extracting sediments from a lost casing (with or without integratedgravel packing), this system requiring a rigid tubular extension loweredby cable and anchored in a suitable receptacle to the bottom of theproduction tubing. A continuous flexible tube known as "coiled tubing"is lowered through this extension, carrying at its end nozzlesdistributing cleaning fluid which is supplied from the surface and theflow of which is directed towards the wall of the well bottom. Thesediment is entrained in the stream of fluid pumped to the surfacethrough the flexible tube, or more precisely the sediment rises to thesurface through the annular space between the coiled tubing and theproduction tubing.

In a system of this kind the addition of this tubular extension to theproduction tubing and the use of the coiled tubing technique comprisinga continuous flexible tube bring about an increase in the speed of thefluid and thus improve the evacuation of sediment via the annular spacebetween the coiled tubing and said extension.

Nevertheless, this system has disadvantages.

A first disadvantage consists in that the circulation of the cleaningfluid exerts a back-pressure on the stratum, which is often friable andvery sensitive (loss, emulsion, precipitate, etc.)

A second disadvantage consists in that the method requires a preliminarycable operation, the limitations of which in respect of length, load anddeviation are well known.

A third disadvantage relates to formations under subhydrostaticconditions or depleted formations; through the back-pressure which itdevelops the system makes it necessary to use prepared fluids of lowrelative density which are compatible with the formation; this may thenbecome prohibitive.

The extensive development of deviated and highly deviated wells andhorizontal drains poses numerous new problems in connection withcleaning through the simple fact that the direction and speed of flow ofthe fluid evacuating solid matter by known, conventional methods andapparatus cannot oppose the forces tending to disintegrate the stratum.

From U.S. Pat. No. 4,744,420 an apparatus is thus also known forremoving solid accumulations, such as sandy or other aggregates, fromhighly deviated or horizontal underground wells. This apparatuscomprises a train of concentric tubes intended to be inserted into thewell, one of said tubes being used to supply the working fluid to thewell bottom and the other for returning the fluid loaded with sediment.At the end of the train the apparatus is also provided with ahydroejector which projects a part of the working fluid onto thesediment before applying suction to it.

Apart from the disadvantages already mentioned, the tube train isinjected into the well after the existing completion has beendismantled. In addition, the apparatus cannot work continuously on alarge area of accumulated sediment without extensive intervention, suchas the addition of extra concentric tubes.

The use of this method disturbs the completion, and this is a majordisadvantage.

SUMMARY OF THE INVENTION

In order to obviate these disadvantages the present invention provides acleanout method according to which a small diameter maintenance tubing,known as "coiled tubing", is lowered into the production tubing,carrying at its end a cleanout head for extraction by suction of thesediment; at a certain level above the part of the well which is to becleaned out a hydraulic separation is made in the annular space betweenthe maintenance tubing and the production tubing, said maintenancetubing being axially slidable in said hydraulic separation over a lengthat least equal to the total length of the part of the well which is tobe cleaned out; and into said annular space a working fluid is injectedfor the operation of a hydroejector which applies suction to thesediment to extract the latter through the maintenance tubing, saidhydraulic separation isolating the pressurised annular space from thewell bottom under reduced pressure.

According to this method, therefore, suction is applied to the sediment,and this suction thus eliminates all the disadvantages due to thepressure exerted on the stratum by the returning fluid charged withsediment.

Furthermore, as the hydraulic separation isolates the well bottom, theworking fluid need not be compatible with it.

According to a preferred embodiment of the invention this hydraulicseparation is effected with the aid of a stuffing box mounted on themaintenance tubing for sliding when the apparatus is in the cleaningposition, said stuffing box cooperating with a landing nipple on theproduction tubing in order to make a sealing, sliding separation.

An arrangement of this kind constitutes a considerable advantage overthe prior art, because the application of the method according to theinvention does not disturb the existing completion. It is in fact onlynecessary for the existing completion to have a landing nipple towardsthe base of the production tubing for the positioning of the hydraulicseparation.

According to another likewise preferred embodiment of the invention themaintenance tubing is a so-called "coiled tubing" of a diameter smallerthan or equal to 38 mm. The coiled tubing is flexible, and by this meansthe method can be applied without discrimination to vertical wells,deviated wells, highly deviated wells, or horizontal drains. The coiledtubing is remarkable in that it makes perfect contact with the bottomgeneratrix of a highly deviated or horizontal drain.

The stuffing box preferably comprises a series of seals on its insidediameter in order to permit sealing sliding of the maintenance tubing onsaid stuffing box.

The stuffing box is shaped to bear against a shoulder on the landingnipple, and also comprises outside seals applied against the insidesurface of said landing nipple. It is held in this position by theelevated pressure during operation.

The cleanout is then effected in one or more progressive passes bymoving the cleanout head in the part of the well which is to be cleanedout, by sliding the maintenance tubing through the hydraulic separation,that is to say by sliding the tubing through the stuffing box.

The cleaning apparatus comprises a cleanout head mounted on the end ofan extension of the maintenance tubing, a stuffing box mounted forsliding on said extension above said cleanout head, and a hydroejectormounted at the other end of said extension, the outlet of thehydroejector being connected to the surface by the maintenance tubing.

The cleanout head has an outside diameter smaller than the insidepassage diameter of the landing nipple, while the stuffing box has anoutside diameter larger than the inside passage diameter of the landingnipple, so as to be locked in respect of translation on said landingnipple.

On its insertion into the well, the stuffing box is provisionally lockedin respect of translation on the cleanout head by means of a pin or anyother equivalent means, which can be broken by elevated hydraulicpressure or a mechanical support on arrival in the landing nipple.

The cleanout head comprises an ejectable stopper closing the externalfluid admission to the maintenance tubing, the ejection of the stopperbeing brought about by elevated pressure in the maintenance tubing.

The utilisation of an intervention technique which is well known andwidely used, such as the coiled tubing technique, is a considerableadvantage. The present invention does not relate to that technique initself, it being known that said technique requires surface apparatus,known per se, such as a blow-out preventer (B.O.P.), a lock chamber, acoiled tubing storage drum, an injector and pumping means, all of whichwill not be described in detail and will not be illustrated within theframework of the present patent application.

It is also another object of the present invention to provide method ofcleaning out which comprises the complete lowering of the maintenancetubing, according to which:

the extension--together with the cleanout head mounted at its end--isinserted under the packer or stripper of the coiled tubing, the stuffingbox being fastened to the cleanout head;

the extension is suspended in the blow-out preventer and the jaws areclosed around the tubing;

the lock chamber is opened;

the coiled tubing is cut;

the hydroejector is inserted with the aid of rapid action connectors;

the lock chamber is closed;

the jaws of the blow-out preventer are opened;

the lowering of the coiled tubing is continued until the stuffing box isengaged in the landing nipple fastened to the production tubing, thesecuring pin being sheared through;

the stopper is ejected from the head by elevated pressure in themaintenance tubing;

the working fluid is injected into the annular space between theproduction tubing and the coiled tubing (and therefore above thehydraulic separation) in order to start up the hydroejector;

the progressive lowering of the cleanout head is continued whileobserving the return of sediment to the surface.

BRIEF DESCRIPTION OF THE DRAWING

Other advantages and features of the present invention will emerge fromthe description given below of one non-limitative example of embodimentof the invention and accompanied by the drawings, in which:

FIG. 1 shows the apparatus for cleaning out a well bottom being loweredinto the well,

FIG. 2 shows the same apparatus in the cleanout position in the well,

FIG. 3 shows the stuffing box of the apparatus shown in FIGS. 1 and 2,

FIG. 4 shows an exemplary embodiment of the cleanout head, with itsejectable stopper,

FIG. 4a shows an exemplary embodiment of the outer face of said cleanouthead, which is adapted to be rotated by the fluid drawn in,

FIG. 5 shows an exemplary embodiment of the obturator connector used forwithdrawing the hydroejector after the cleanout operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 of the drawings the reference 1 designates a continuous tubeof relatively small diameter, which is smaller than or equal to 38 mm(11/2 inch). This tube is the tubing of a tool used for inter-ventionoperations under pressure in production wells, which is known as the"coiled tubing" technique, which is a technique in which a continuousflexible tube stored on a drum is injected into a well under pressure.This technique is suitable for any configuration of well head and allowsspeedy operation. The injection system, comprising in particular theblow-out preventer and the lock chamber, and also the coiled tubingstorage system and the fluid injection means and means for pumping tothe surface, are not shown in the drawings.

At the end of the coiled tubing 1 a venturi action pump or hydroejector3 working with reversed pumping is mounted with the aid of a 38 mm (11/2inch) connector 2. A nonreturn valve 3a installed in the venturiprevents any return of liquid to the space surrounding the pump, as willbe explained later on.

By means of an obturator connector given the reference 4, which has adiameter of 38 mm (11/2 inch), the pump 3 is connected to a tubularextension 5, whose diameter is equal to that of the tubing 1 and whoselength is adjustable in dependence on the dimensional characteristics ofthe well which is to be cleaned out. This length is at least equal tothe distance between the selected hydraulic separation level (L in FIG.2 of the drawing) and the most distant part of the well which is to becleaned out.

A stuffing box 6 is mounted for sliding along the tubular extension 5.It is shown in greater detail in FIG. 3 of the drawings. On its insidebore 6a it has a series of lipped O-ring seals 6b and on its outsidebore 6c a series of resilient, compressible lipped seals 6d, the seals6b providing sealing on the tubular extension 5, while the outside seals6d cooperate with a member on the production tubing (the landing nipple)to provide the hydraulic separation, as will be seen further on.

In the lowering position shown in FIG. 1 of the drawings the stuffingbox 6 is locked in respect of translation on the top of a cleanout head7 by means of a pin 8 (see FIG. 3), which can be sheared through underthe conditions described later on in order to enable the maintenancetubing to slide in the inside bore of the stuffing box 6.

The end of the extension 5 is provisionally closed by an ejectablestopper 7a (see FIG. 4), which in its closed position serves to permitthe connection of the pump 3 at the surface.

The cleanout head 7 extending the tubular extension 5 is designed tofacilitate cleaning out by induced rotation and turbulence.

In FIG. 4 of the drawings the cleanout head 7 and its mounting at theend of the tubular extension 5 are shown. The ejectable stopper 7a islocked in the closed position by means of the pin 13. The head ismounted rotatably in a ball bearing 14. A conventional grip connector 18comprising the members 15, 16, 17 enables the head 7 to be fastened ontothe extension 5.

Oblong slots 19, pierced in non-radial directions but directed helicallyor quasi-helically, are provided in the head in order to impart to thecleanout head 7 a rotary movement through the action of the fluidspassing through (FIG. 4a).

Turbulence fins 20 (FIG. 4a) may also be provided on the outer surface.

In FIG. 2 of the drawings the reference 9 represents schematically thecasing of the well, which may be a vertical well, a deviated or evenhighly deviated well, or even a horizontal drain. The production tubingis designated 10. The annular space between the production tubing 10 andthe casing 9 is closed by a packer 11 The cleanout unit or maintenancetubing shown in FIG. 1 is introduced into the production tubing 10,which has a well bottom landing nipple 12 which by its shoulder 12aforms a seat for the stuffing box 6. In the example now being describedthe production tubing 10 may be of any diameter.

The cleanout system operates as follows:

The cooled tubing wound on a drum at the surface is inserted, withoutdisturbing the pressure prevailing at the well head, into apacker-stripper (not shown) with the addition of lubricating grease, andcarries the cleanout head 7 at its free end. The stuffing box 6 isinserted above the cleanout head and is locked in respect of translationto the cleanout head 7 by means of the pin 8 (FIG. 3). The length ofcoiled tubing inserted in this way into the stripper depends on thedistance between the most distant part of the well which is to becleaned out and the position (L) of the landing nipple 12 forming asliding bearing for the maintenance tubing and the hydraulic separation.The length of the tubular extension 5 is equal to or greater than theabove distance.

The coiled tubing is suspended in the jaws of a blow-out preventer(B.0.P.), and the lock chamber is opened. This conventional equipmentfor the coiled tubing technique is not illustrated in the drawings andwill not be described in detail.

The coiled tubing is cut at the surface, safety being ensured by theposition of the ejectable stopper 7a in the cleanout head 7, preventingany flow-back of fluid through the coiled tubing forming the maintenancetubing.

In a manner known per se the hydroejector 3 is inserted with the aid ofan obturator connector 4 shown in FIG. 5 of the drawings. This connector4 comprises a quarter-turn valve 4a housed in a bore 4b and adapted tobe oriented by means of a pin 4c. This type of connector also comprisesa plurality of seals 4d and an outer surface having a curvilinearprofile into the indentations of which the tubular parts of the membersto be connected are crushed by force (FIG. 5).

The lock chamber is reconnected, the jaws of the blow-out preventer areopened, and the lowering of the coiled tubing, joined to thehydroejector 3 by means of the connector 2--likewise of 38 mm (11/2inch), is continued so as to form the tubular part designated 1 in FIGS.1 and 2 of the drawings.

When the stuffing box 6 reaches the level of the hydraulic separationposition L, and is thus engaged in the well bottom landing nipple 12,pumping of the working liquid into the annular space between theproduction tubing 10 and the maintenance tubing 1, 2, 3, 4, 5, 6, and 7can start; the pressure of the working liquid enables the stuffing box 6to bear perfectly against the seat 12a of the landing nipple 12 and tobe locked thereon in respect of translation. Hydraulic separation isachieved, and the part of the production tubing situated below thehydraulic separation (designated LB) and, consequently, also the wellbottom are isolated from the annular space under elevated pressure (LH)situated above the hydraulic separation.

This hydraulic separation constitutes an important feature of thepresent invention. This separation in fact permits the movement and theevacuation of the sediment without elevated pressure being exerted onthe stratum and without contact between the working fluid and the wallof the well. Cleanout operations are effected while the part of the wellwhich is to be cleaned out is isolated by the hydraulic separationachieved through the locking of the stuffing box 6 on the landing nipple12 at the location L.

It will also be noted that neither the application of the method itselfnor the creation of this separation requires the addition of extraequipment or the modification of existing equipment in the completion.

By means of elevated pressure in the maintenance tubing the ejectablestopper 7a is ejected (shearing of the pin 13 or any other means knownper se) and falls to the bottom of the cleanout head 7, and the wellbottom is then connected to the surface (see FIG. 4).

The working fluid pumped from the surface brings into action the suctionof the hydroejector 3 by way of the cleanout head 7 and the tubularextension 5.

Further lowering of the coiled tubing then shears the pin 8 securing thestuffing box 6 on the cleanout head 7. The coiled tubing can then beprogressively pushed to bring the cleaning head 7 close to the parts ofthe well which are to be cleaned out, the extension tube 5 sliding forthis purpose in the inside bore 6a of the stuffing box 6.

The sediment is sucked through the apertures 19 in the cleanout head,and rise through the extension tube 5, the connector 4, the hydroejector3 and the tubing 1 to the surface.

The cleanout head 7 may be a rotary head having a cyclone action throughthe arrangement of the apertures in helical lines, as already mentioned.

A plurality of passes may be made by maintaining the elevated pressureon the stuffing box 6 against the seat 12a of the landing nipple 12.

At the end of the cleanout operation the working fluid is replaced by afluid which is non-polluting for the tank and which may or may not havea stabilising action on the well. If this fluid is a gas, the well willgenerate a head pressure. In this case the maintenance tubing is closedinternally when it arrives at the surface by means of an obturator 4ahoused in the connector 4 placed under the hydroejector 3, thuspermitting the retraction of the hydroejector and the rejoining of thecoiled tubing in order to continue the extraction of the latter undercontinuous pressure.

Finally, an additional advantage of the method according to theinvention will be noted, namely the fact that any leakage defect at thestuffing box will not jeopardise the cleanout method, but will simplyresult in reduced energy efficiency, which can be made good byincreasing the flow of working liquid.

I claim:
 1. A method of cleaning out a vertical, deviated or horizontalunderground well equipped with production tubing, comprising the stepsof:lowering maintenance tubing into an interior of said productiontubing; carrying with said maintenance tubing, means including acleanout head and a hydroejector for extracting sediment by suctionthrough the maintenance tubing, said cleanout head being carried at anend of said maintenance tubing; effecting a hydraulic separation in anannular space between the maintenance tubing and the production tubingat a certain level above a part of the well which is to be cleaned out;injecting into said annular space a working fluid for operation of thehydroejector, said working fluid pressurizing said annular space andsaid hydraulic separation isolating the pressurized annular space fromthe well bottom, said well bottom being under reduced pressure; andmoving the cleanout head by sliding the maintenance tubing through thehydraulic separation in the part of the well which is to be cleaned out.2. A method of cleaning out an underground well as claimed in claim 1,wherein said step of effecting a hydraulic separation comprises the stepof effecting the hydraulic separation by means of a stuffing box mountedfor sliding on a tubular part of the maintenance tubing, said stuffingbox cooperating sealingly and by the matching of shapes with a landingnipple on the production tubing at the hydraulic separation.
 3. A methodof cleaning out an underground well as claimed in claim 1, furthercomprising the step of forming the maintenance tubing from "coiled"tubing having a diameter smaller than or equal to 38 mm.
 4. A method ofcleaning out an underground well as claimed in claim 3, wherein saidstep of effecting said hydraulic separation by means of a stuffing boxcomprises the steps of providing a stuffing box shaped to bear againstthe landing nipple;locking said stuffing box on said landing nipple withrespect to relative translation between the landing nipple and stuffingbox; and applying outside seals against an inside surface of saidlanding nipple so as to effect a leak tight hydraulic separation. 5.Cleanout apparatus for cleaning out a vertical, deviated or horizontalunderground well equipped with production tubing, comprising meansincluding maintenance tubing for lowering into an interior of saidproduction tubing, said maintenance tubing carrying means including acleanout head for extraction of sediment by suction, said cleanout headbeing carried at an end of a tubular extension of said maintenancetubing;means for injecting a working fluid for operation of ahydroejector into an annular space between the maintenance tubing andthe production tubing at a certain level above the part of the wellwhich is to be cleaned out, thereby pressurizing said annular space;means for effecting a hydraulic separation in the annular space, saidhydraulic separation isolating the pressurized annular space from thewell bottom, said well bottom thereby being under reduced pressure; andmeans for moving said cleanout head in the part of the well which is tobe cleaned out by sliding the maintenance tubing through the hydraulicseparation.
 6. Apparatus as claimed in claim 5, wherein said means foreffecting the hydraulic separation comprises a stuffing box mounted forsliding on said tubular extension above said cleanout head; and saidhydroejector which is mounted at a second end of said extension, theoutlet of the hydroejector being connected to an above ground surface bysaid maintenance tubing, said maintenance tubing comprising "coiled"tubing.
 7. Apparatus as claimed in claim 6, further comprising a landingnipple arranged to cooperate with said stuffing box to effect saidhydraulic seal, said landing nipple being positioned on the productiontubing, and wherein said cleanout head has an outside diameter smallerthan an inside passage diameter of the landing nipple.
 8. Apparatus asclaimed in claim 7, wherein said stuffing box has an outside diameterlarger than an inside passage diameter of the landing nipple, saidstuffing box abutting against the landing nipple.
 9. Apparatus asclaimed in claim 6, wherein the stuffing box is provisionally lockedwith respect to translation on said tubular extension by means of a pinarranged to be broken by elevated hydraulic pressure on a top face ofsaid stuffing box.
 10. Apparatus as claimed in claim 5, wherein saidhydroejector has a reduced outside diameter of between 50 and 63 mm andincludes means comprising an integrated non-return valve for preventingreturn of liquid to the annular space between the production tubing andthe maintenance tubing.
 11. Apparatus as claimed in claim 5, wherein thecleanout head comprises means including an ejectable stopper for closingfluid admission to the maintenance tubing, said stopper being arrangedto be ejected as a result of elevated pressure in said maintenancetubing.
 12. Apparatus as claimed in claim 5, wherein said cleanout headis a rotary head having a cyclone action.
 13. A method of cleaning out avertical, deviated or horizontal underground well equipped withproduction tubing, said method being carried out with the aid of acoiled tubing installation comprising coiled tubing wound on a drum, alock chamber, and a blow-out preventor, and said method comprising thesteps of:inserting the coiled tubing, together with a stuffing box and acleanout head located at an end of said coiled tubing, into the packeror stripper of the coiled tubing, said stuffing box being provisionallyfastened to the cleanout head with respect to translation; lowering thecoiled tubing into the production tubing; suspending the coiled tubingin the blow-out preventor; opening the lock chamber; cutting the coiledtubing at a distance at least equal to a distance between a hydraulicseparation and the furthest part of the well which is to be cleaned out,said hydraulic separation being effected in an annular space between themaintenance tubing and the production tubing at a certain level abovethe part of the well which is to be cleaned out; inserting ahydroejector with the aid of connectors; closing the lock chamber;opening jaws of the blow-out preventor; continuing lowering of thecoiled tubing until the stuffing box is engaged in a landing nipplefastened to the production tubing; opening communication between thecleanout head and the coiled tubing connection in order to suck thesediment to the surface; injecting working fluid into the annular spacebetween the production tubing and the coiled tubing in order to start upthe hydroejector; and continuing to lower the cleanout head after it hasbeen disconnected from the stuffing box.